A skull that was discovered in Placer County nearly four decades ago was recently identified through relational DNA tracing, and investigators say it belongs to a young woman who disappeared from a Lake Tahoe casino hotel in 1970.

How many victims did the Zodiac Killer actually kill? It's a question that remains as open as the bigger question of who was the Zodiac Killer, a question which has not been solved, frustratingly, 55 years after his last known murder. The man who killed at least five people in the Bay Area may have killed dozens more, and investigators around California have been trying to pin unsolved murders to the Zodiac for decades.

One such case was Donna Lass, a 25-year-old nurse who was employed by the Sierra Tahoe Casino hotel in Stateline, Nevada (now the Golden Nugget). Lass worked nights, and on September 6, 1970, she made her last entry in a log book at 1:50 a.m. and got off work at 2 a.m. No one actually saw her leave the casino.

She had rented an apartment in South Lake Tahoe that she had not yet moved into, and investigators had a report that she was seen outside of it with a young blond man.

Still, Lass disappeared without a trace, and the only evidence that authorities had that something might be wrong were two phone calls later on September 6, from a man, telling both her landlord and her boss at the casino that she needed to leave town on a family emergency. Lass's family told investigators there was no such emergency.

Six months later, in March 1971, the SF Chronicle — which had been a repository for messages from the Zodiac, many of them written in code — received a postcard from Lake Tahoe that seemed to suggest he had killed "Victim 12" in the Tahoe area. Investigators quickly tied this postcard to Lass's disappearance.

The postcard, like some of Zodiac's other missives, featured a collage of magazine letters and images, including an ad for the newly built Forest Pines Condominiums in Incline Village, NV. It said "peek through the pines" and "pass Lake Tahoe areas" and "around in the snow."

An image of the original postcard believed to have come from the Zodiac Killer in March 1971.

Over four years after Lass's disappearance, in December 1974, Lass's sister, Mary Pilker, received a Christmas card at her home in South Dakota that also featured snow-covered trees, and contained the message, "Best Wishes, St. Donna & Guardian of the Pines." The card was postmarked from the Bay Area.

The skull that Placer County authorities found was discovered in 1986, off of Highway 20 near I-80, and it was set aside for later identification — with DNA technology not available at the time. Nothing else was found with the skull.

South Lake Tahoe Police Chief David Stevenson told KCRA last week that familial DNA had finally cracked the case of the identity of the skull, thanks to "a brand-new cold case team, made up of people from the Placer County Sheriff's Office and Placer County District Attorney's Office." That team apparently only got to work a month or so ago.

It's unclear why it took quite so long, but DNA from the skull was just recently linked to a DNA sample taken five years ago from Lass's sister.

"They had those remains sampled for DNA," Stevenson told the station. "It was processed, run through the system and CAL DOJ was able to get a hit on those remains based on that familial DNA that was uploaded."

"Obviously it was a long time ago, but families never forget," Stevenson added. "It never gets old. It never goes away. They never heal. That unknown is very painful for them."

The case still has not been proven to be a homicide, and investigators are looking for any leads they can find. Anyone with information is asked to call the South Lake Tahoe Police Department or email [email protected].

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